Manufacture of high octane gasoline



March 9, 1943.

C. W. MONTGOMERY MANUFACTURE OF HIGH OCTANE GASOLINE Filed May 23, 1940 Patented Mar. 9, 1943 UNE'E'E STES ArtNr OFFICE MANUFACTURE F HIGH OCTNE GASULIN Application May 23, 1940, Serial No. 336,884

` s claims. (ci. iasimg y This invention relates to the manufacture of high octane gasoline; and it is particularly concerned with an improved process of producing high octane gasoline comprising treating an lsoparain with an olen in the presence of a coni densation catalyst, separating the higher boiling iso-paraidns from the gasoline-like material thus formed, dehydrogenating the undesirably high boiling iso-paraiins to form iso-olens and reacting the iso-olens thus obtained with lower molecular weight iso-paraiiins to form further quantities of high octane gasoline; all as more fully hereinafter set forth and as claimed.

Among the more recently developed methods for the production of high octane gasoline substantially free from unsaturated gum forming constituents is a method in which the lower isoparains (iso-alkanes) such as iso-butane, isopentane and the like, are condensed With the lower olens in the presence of a suitable catalyst such as concentrated sulfuric acid or an aluminum halide usually at or about room temperature. The initial reaction which takes place is a direct union of the iso-parain with the olen to form a high molecular weight iso-paraiiln; for example, iso-butane combines witha butene to form iso-octane. Secondary reactions also occur resulting in the production of both higher and lower hydrocarbons. The end-product is a mixture of higher and lower hydrocarbons boiling substantially within the gasoline range, having a high octane rating and being substantially free from unsaturates. When the process is carried out in batch operation about 20 per cent of the end-product boils above the ordinary gasoline range, that is above about 185 C., and it consists essentially oi higher boiling iso-parains. In a continuous process there is usually only a small percentage of iso-params boiling above this point.

The gasoline product obtained by this process is particularly suitable for use as an aviation gasoline because of its high octane rating and its freedom from gum forming constituents. A particularly good fighting grade? aviation gasoline suitable for use in military and naval airplane motors can be obtained by taking the fraction of these products boiling up to 165 C. When lighting grade aviation gasoline is produced, about 25 per cent of the product of a continuous alkylation process boils above the 165 C. endpoint and a correspondingly increased proportion of the product obtained by a catch process boils above this end-point. I have newl discovered that these higher bolling lso-paraflins forming the fraction of the alkylation reaction product boiling above 165 C. react relatively slowly with olefins but that by dehydrogenating them to form iso-olens and reacting the high molecular weight iso-olens thus obtained under the conditions of the alkylation reaction, with short chain iso-parains, further quantities of mixed saturated hydrocarbons boiling Within the gasoline range can be produced.

In carrying out the method of my invention I rst alkylate an iso-parailin, usually au iso-paraliin containing four to six carbon atoms, with an olen by passing a mixture of gases containing the olen in suitable proportion int'o a mixture of the iso-paramn and a catalyst such as concentrated sulfuric acid or aluminum chloride at or about room temperature, usually under pressure. The ratio of iso-paraflin to olen is advantageously maintained at a relatively high level in order to avoid polymerization of the ole.- n. 'Iso-paraiiin to olen ratios of between 2:1 and 10:1 have proved satisfactory.V

The choice of catalyst depends usually on the olelin with which the reaction is carried out. When lower oleflns such as ethylene or propylene are used it is generally desirable to use an aluminum halide catalyst such as aluminum chloride. These lower olens, particularly ethylene, are comparatively unreactive and it is diflicult to effect alkylation with them. However, the aluminum halide catalysts are suiciently powerful to effect the desired reaction. In most other cases it is advantageous to use concentrated sulfuric l acid as the catalyst. Most satisfactory results are obtained usingY 85.0 to 98.0 per cent sulfuric acid.

The alkylation reactionv may be carried out either in batch or continuous operation. In most cases it has been found advantageous to .introduce the olefin into a rapidly agitated mixture of the catalyst and the iso-paraflin in an kali solution to remove acid and acid-formingA components. The Washed product is fractionally distilled and the fraction boiling within the normal gasoline boiling range is collected. For

ghting grade aviation gasoline the end-point used is usually about 165 C.

According to the method of my invention, the

higher boiling iso-parafiins remaining after the quantities of gasoline boiling within the 'desired' range.

The dehydrogenation of the residual iso-parafrlns may be carried out by various known methods. One method which I have found suitable for this purpose is to contact the iso-paraffin with a catalyst such as chromic oxide gel at a temperature of '400 to 600 C. Other catalysts may also be used for this dehydrogenation such as the oxides of molybdenum, tungsten, and vanadium. Dehydrogenation activity of these catalysts is usually promoted by supporting the oxides on activated alumina which also serves to increase the contact area. The materials employed as catalysts for the dehydrogenation are also effective catalysts for aromatization of the parafnns containing more than six carbon atoms. However, the iso-paraillns undergo this type of reaction relatively slowly so that by limiting the time of contact of the iso-paralns with the catalyst the extent of all reactions except dehydrogenation can be greatly reduced. 'I'his may also be accomplished by employing less active catalysts as for example by reducing the content of chromic oxide in an activated alumina supported chromic oxide catalyst preferably below 5 per cent, or even by employing activated alumina alone without any addition of heavy metal oxides. Activated alumina by itself appears to produce considerably less aromatlzation than chromic oxide on alumina.

In carrying out the dehydrogenation step, the heavy iso-paraiilns boiling above the desired endpoint of the aviation gasoline are first separated by appropriate fractionation. They are then pumped through a suitable heat exchanger, vaporized in a preheater and passed into the dehydrogenation reactor which may be packed, for example, with activated alumina pellets as such or supporting 1 to 5 per cent chromic oxide. The reaction zone is preferably maintained at about 500 to 600 C. in case alumina is used alone as the catalyst, or at somewhat lower temperatures, say 400 to 500 C. when supported heavy metal oxides are employed. The optimum contact time in the reactor will, of course, vary with the activity of the catalyst but will usually be found to lie in the range 1 to 20 seconds. Pressure is advantageously maintained` at 1 to 4 atmospheres. Operation under these conditions has been found to yield predominately iso-olens (15 to 30 per cent per pass) with considerably smaller amounts (1 to 3 per cent per pass) of aromatics.

'I'he high molecular weight iso-oleilns-thus obtained are then treated with further quantities of low molecular weight iso-parafllns in the presence of sulfuric acid or other allavlatlon catalyst and an additional quantity of gasoline is recovered as before from the reaction product.

Thus by the method of my invention, larger amounts of gasoline suitable for use in airplane motors are recovered from a givenamount of raw material than`has heretofore been obtainable. a

In the accompanying drawing there is illustrated schematically a suitable apparatus for carrying out the method of myinvention. In this apparatus there is provided alkylator l0 into which the isoparailln charge is introduced through conduit il in admixture with the catalyst from conduit l2. The olefin containing charge is introduced into the top of the alkylator I0 through conduit Il. The alkylation reaction g between olefin and isoparailln is effected with vigorous agitation in the alkvlator i0. -The alkylate from alkylator l0 is conducted by conduit I4 to separator I5 where the catalyst is settled out and recycled through conduit I6 to conduit i2 and the alkylator l0.

lThe alkylate from separator I 5 is carried by conduit l1 to alkali washer i8 where any remain-` ing acid catalyst is removed. The washed alkylate is then conducted by conduit I8 to frac.- tionating column 20 where the unreacted excess isoparafilns are distilled of! and recycled through conduit 2| to conduit II and reintroduced into the alkylator. The alkylate from the bottom of column 20 is conducted by conduit 22 to a second fractionating column 23 where the gasoline fraction is distilled oi'f through conduit 24 andy recovered. The heavy isoparailln bottoms from column 23 are conducted through conduit 26 to heat exchanger 26 and conduit 21 to heater 23 where they are heated and vaporized.

The Visoparailln vapors are conducted from heater 28 through conduit 29 to the dehydrogenator 30 where they are contacted with the dehydrogenating catalyst. The dehydrogenation reaction products are conducted by conduit 3l to gas separator 32 where the hydrogen is separated and recovered through conduit 33. The high boiling olefins resulting from the dehydrogenation of the heavy isoparafiln are drawn olf from gas separator 32through conduit-34 and are introduced into -alkylator 35 where they are mixed with fresh isoparaill'n/charge, and catalyst from conduit 31, introduced into alkylator 35 through conduit 38. The alkylate formed is drawn oi through conduit 33 to separator 39 where the l then introduced into fractionating column 44 through conduit 43 and the unreacted isoparailln is taken off overhead and recycled to the alkylator 35 through conduits 45 and 36. The remaining alkylate is drawn oil! through conduit 48 to fractionating column 41 where additional gasoline is taken oil overhead through conduit 48 and recovered. The heavy isoparaln bottoms are recycled from fractionating column 41 through conduit 49 to conduit 25 where it is reintroduced into the dehydrogenation step of the process.

In an alternative form of this apparatus the high boiling oletlns from conduit 34 are recycled directly to the flrst alkylator l0. In such case the secondalkylator 435 and succeeding apparatus are omitted. The operation of this form of apparatus is, however, somewhat more difllcult to control. The following specic example illustrates one embodiment of my invention in which iso-buing a mixture of C4 hydrocarbons including butane, butene-l, butene-2, and iso-butylene.

Iso-butane was alkylated with debutanizer gas of such composition that the total iso-butanebutene volume ratio was about 4:1. Sulfuric acid of 98 per cent strength was used in a continuous unit and the temperature Was maintained at 18 C. A yield of debutanized alkylate equal to 165I volume per cent of the charged butenes was obtained, 75 volume per cent of which boiled below 165 C. The 25 per cent heavy ends were dehydrogenated over alumina, in the manner described above, at 550 C., atmospheric pressure, and 10 seconds contact time. A 97 volume per cent recovery was obtained, the product analyzing 20 per cent olens. This material was used to alkylate fresh isobutane using an isobutaneoleiin volume ratio of approximately 5:1. Fractionation of the debutanized product yieldedv an additional amount of 165 end-point aviation gasoline equal to 131 volume per cent of the isoolefins produced in the dehydrogenation step.

While my invention has been described herein with respect to certain specic embodiments thereof by Way oi' example, I do not intend that my invention shall be limited to such embodiments or the details thereof except as hereinafter defined in the appended claims.

What I claim is:

1. A process of producing high octane gasoline comprising alkylating an iso-paraffin with an olen in the presence of an alkylation catalyst, washing the reaction product with dilute aqueous alkali to remove acidic and acid-forming constituents, separating the higher boiling iso-parains from the hydrocarbons boiling in the gasoline range by fractional distillation of the washed reaction product, dehydrogenating the higher boiling iso-parafns thus obtained to form iso-olens and alkylating these iso-olefins with further` quantities of lower boiling isoparaflins in the presence of an alkylation catalyst to form additional amounts of hydrocarbons boiling in the gasoline range.

2. In a process of alkylating an iso-paraffin with an olefin in the presence of an alkylation in the presence of an alkylation catalyst, the

improvement comprising separating the higher boiling iso-paraiiins from the fraction of the reaction product boiling within the gasoline range, dehydrogenating these higher iso-paraflins to form iso-olens and alkylating the iso-olefins thus formed with lower boiling iso-paraffinsin the presence of an alkylation catalyst to form further quantities of hydrocarbons boiling within the gasoline boiling range.

4. A process of producing high octane gasoline comprising alkylating an iso-paraflin with an olefin in the presence of a concentrated sulfuric acid, washing the reaction product with dilute aqueous alkali to remove acidic and acidforming constituents, separating the higher boiling iso-parains from the hydrocarbons boiling in the gasoline range by fractional distillation of the washed reaction product, dehydrogenating the higher boilingiso-parafns thus obtained to form iso-olens and alkylating these iso-olens with further quantities of lower boiling iso-paraflins in the presence of a concentrated sulfuric acid to form additional amounts of hydrocarbons boiling in the gasoline range.

5. A process of producing high octane gasoline comprising alkylating an iso-parain with an olefin in the presence of aluminum chloride, washing the reaction product with dilute aqueous alkali to remove acidic and acid-,forming y,

constituents, separating the higher boiling isoparains from the hydrocarbons boiling in the gasoline range by fractional distillation of the washed reaction product, dehydrogenating the higher boiling iso-paraflins thus obtained to form iso-olens and alkylating these iso-olens with further quantities of lower boiling iso-paramns in the presence of aluminum chloride to form additional amounts of hydrocarbons boiling in the gasoline range.

6. A process of producing aviation grade gasoline comprising alkylating an iso-paraffin with an olefin in the presence of an alkylation catalyst, fractionating the alkylation products to form gasoline boiling below about C. and a higher boiling iso-paran-fraction, dehydrogenating the high boiling iso-paraflins thus separated to form high molecular weight iso-olefins, and alkylating said iso-olens with further quantities of a lower boiling iso-paraflin to form additional amounts of hydrocarbons boiling in the aviation gasoline boiling range.

CHARLES W. MONTGOMERY. 

